Flexible expandable roller conveyors which utilize lazy tong support frames or structures have been widely used for many years. Lazy tongs are structures formed of a set of parallel bars, most of which are pivotally connected at their end points and midpoints, to corresponding bars in a transversely oriented set of parallel bars so that the structure may be extended and retracted with scissor-like action. Such structures for conveyors are disclosed in U.S. Pat. No. 3,276,558 issued Oct. 4, 1966 to Guske, et al. and U.S. Pat. No. 4,266,650 issued May 12, 1981 to Patel, et al., which are both incorporated herein by this reference. The conveyors of those patents include lazy tong structures which are connected by a number of axles or rods, each of which carries several rollers. Such conveyors are sometimes known as "skate wheel" conveyors because the rollers are, or are similar in construction and appearance to, roller skate wheels.
U.S. Pat. No. 4,852,712 issued Aug. 1, 1989 to Best discloses another form of gravity roller conveyor utilizing lazy tong structures which include, among other things, additional support for the skate wheels. That document is incorporated herein by this reference. These durable conveyors are particularly useful to move packages and other items from one point to other points in the plant or warehouse and in loading or unloading trucks, airplanes, or containers. They may be flexed and extended or retracted with minimum effort to accommodate the desired location, vehicle, or container.
The nature of the lazy tong structure allows such conveyors to be retracted and stored in a compact fashion in which successive axles and rollers are positioned nested together immediately adjacent to one another. The distance between successive axles and rollers increases as the conveyor is expanded to its operative position for conveying articles. The expandable and retractable nature of such conveyors has conventionally precluded using a drive belt for moving articles, so that workers are typically required to propel articles carried by the conveyors manually or to rely upon gravity.
For many years, rigid, non-lazy tong conveyors have employed elongated, tubular-shaped rollers instead of skate wheels for various materials handling purposes in applications such as those, for instance, where articles are shaped or configured inappropriately for conveyance on skate wheel surfaces. There have also been motorized or powered variations of such conveyors to address situations where gravity conveyors are inappropriate. Such motorized elongated roller conveyors have, in the past, employed polymeric or plastomeric tubular belts around the elongated rollers for applying power to rotate the rollers.